Crack branching in cross-ply composites: an experimental study

The objective of this research is to discuss experimental data regarding a type of failure called crack branching. The specimens tested are layered glass/epoxy and graphite/epoxy cross-ply composites, manufactured with an initial interlayer crack. Experiments were carried out under static conditions. A designed two-level twovariable experiment based on an 8×8 Hadamard matrix was performed in order to identify the key parameters of the phenomenon. Moreover, a smoothing technique (smoothing by running median of 3 repeated) was used to interpret the crack growth rate in terms of branching angles. The results indicate that there is a critical branching angle (39¯40°). When the crack branches with an angle greater than this critical value, the crack growth rate increases with the branching angle. Moreover, the branching angle increases when the initial delamination decreases, for branching angles greater than the critical value. The position through the thickness does not seem to significantly affect the branching angle